EDWARDS, Thea M.; BENSON, Neal; THRO, Matt; TOFT, Gunnar; GUILLETTE, Louis J.; University of Florida, Gainesville; University of Florida, Gainesville; University of Florida, Gainesville; University of Florida, Gainesville; University of Florida, Gainesville: Reduced sperm quality and seasonal reproductive variation in male Gambusia holbrooki (Eastern Mosquitofish) collected from contaminated versus reference lakes in Florida

As an early step in developing Gambusia as an endocrine disruption model in Florida, we collected adult males monthly for 19 months from two lakes. Lake Apopka is eutrophic and contaminated with several known endocrine-disrupting chemicals; Lake Woodruff is relatively pristine, and served as our reference site. Our monthly reproductive endpoints include hepato- and gonadosomatic index (GSI), hormone concentrations, and sperm counts and viability (percent live). Males from both lakes produced sperm year-round, although hormone concentrations and sperm quantity and viability varied seasonally. In most months, males from Lake Apopka had significantly higher GSIs relative to fish from Lake Woodruff. This was associated with no difference in sperm counts, except in February and early September, when males from Lake Apopka exhibited decreased sperm counts compared to males from Lake Woodruff. In addition, sperm viability was higher in males from Lake Woodruff in November, January, and June. Reduced sperm quality in males from Lake Apopka does not appear to negatively affect reproduction at the population level, since Apopka females collected at the same time actually produced three times as many offspring as their Woodruff cohorts. However, as a possible example of endocrine disruption, our data suggest subtle changes in male fertility that warrant closer examination.